Richard Fry wrote:
Roy Lewallen's post of Dec 29, 9:45 pm generally supports the points I
have been writing about.

That surprises me. Apparently I didn't understand your points, which
seem to emphasize the importance of considering the field very close to
the antenna in evaluating an antenna's performance for long-distance
skip communication. The data I posted show clearly that this isn't so,
because that strong field at low angles is attenuated to virtually zero
well before it can reach the ionosphere. The low elevation angle field
close to the antenna is of interest only if the other station is close
to the antenna.

But two observations are due:

Fortunately for the broadcasters, the surface wave component
doesn't detach itself from the Earth and head for the ionosphere
as the Earth curves away, but follows the curvature of the Earth.
This allows broadcasting beyond the horizon without ionospheric
skip, and prevents fading from the ground wave alone. It doesn't
reach the ionosphere as Richard has claimed.

The last sentence above is incorrect in that I made no such claim. My
post stated only that radiation from elevation angles as small as one
degree will reach the ionosophere. See the paste below.

Sorry, I interpreted your postings to state that the surface wave was an
important factor to consider in determining the strength of the field
from a vertical for working skip communication. If that's not what you
meant, then exactly what is the point you were trying to make regarding
the importance of considering the surface wave for amateur communication?

"But that isn't the case -- the relative field over real ground at low
elevation angles close to the vertical radiator can be very high, and
will continue onward to produce a long-range skywave. Even radiation
at an elevation angle of one degree will reach the ionosphere, due to
earth curvature."

The data I gave shows this to be incorrect. While the field at low
angles close to the radiator are very high, they don't "continue outward
to produce a long-range skywave". The very low angle field, as I've
shown, decays rapidly with distance and is virtually gone well short of
the distance needed to reach the ionosphere. From the data, at one
degree elevation angle, the surface wave has decayed to nearly zero
within 50 miles of the antenna (the difference between sky wave +
surface wave and sky wave only is 0.8 dB), and at 7 MHz, within 10
miles. This means that the surface wave makes no contribution to the one
degree elevation angle wave reaching the ionosphere. So there's no point
in calculating or considering the surface wave if your interest is in
ionospheric, or anything other than ground wave, communication.

A low elevation angle does not include zero degrees (the horizontal
plane).

Ok.

The reported field strengths are in dBi for easy comparison; ...

The term "dBi" is not a unit of field strength. Field strength is a
voltage existing between two points in space typically one meter
apart, and is expressed in terms of that voltage with respect to that
distance, as in volts/meter (V/m).

dBi is a direct expression of field strength, but normalized for power
and distance. At any particular distance and power level, for any field
strength in V/m there is only one corresponding value of dBi, and
vice-versa. I gave the conversion equation in my posting.

Field strengths can be compared using decibels, but such comparisons
are referenced to the field strength shown in standard form. For
example, a field strength of 1,000 µV/m may be expressed as 60 dBµV/m.

dBi is more than just dB. It's field strength (in dB) relative to a
known standard. That enables direct calculation of field strength in V/m
for any power level and distance, given the dBi value.

But that's really beside the point. Anyone with a calculator and the
posted equation can quickly convert the table I gave into V/m for
whatever power level you'd like. The conclusions are the same.

Roy Lewallen, W7EL